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I do not know about a Microbus auto gearbox, but the automatic 411 and 412 Variants had a microswitch below the accelerator pedal, if you would 'floor' it it would close the circuit for a solenoid on the gearbox to select a lower gear.
That looks to be a vacuum kick down and will pull a link in the gearbox to allow the box to kick down.
If you floor the petrol, you cause a high vacuum, and this will tell the box to step down one or more gears.
Herman
1968 Fastback 2Lt.type4
1972 Low Light Bay Panel Van 2Lt type 4
1975 Fleetline Panel Van 1914cc
2020 MeFusco Beetle "Bakkie" 2Lt type 4
1972 FT Hahn SP 1776 cc
Without vacuum, it should be not pulling, but all slack taken up.
Herman
1968 Fastback 2Lt.type4
1972 Low Light Bay Panel Van 2Lt type 4
1975 Fleetline Panel Van 1914cc
2020 MeFusco Beetle "Bakkie" 2Lt type 4
1972 FT Hahn SP 1776 cc